Beneficial uses of microorganisms are well known in the art and have been documented at great length. Many patents have issued which claim new microbial processes pertaining to the production of antibiotics, enzymes, ethanol, and a multitude of other useful products. Microorganisms are also used to clean up toxic wastes and oil spills, kill pests, recover minerals, and provide nutrients to plants. It has been known for many years that some organisms produce compounds which are toxic to other organisms. The production of the antimicrobial compound penicillin by penicillium mold is one such example.
Microorganisms are particularly attractive candidates for use in making and delivering organic compounds because they can be extremely efficient and safe. The modern tools of genetic engineering have greatly enhanced the ability to exploit the efficiency and relative safety of microbes. Even in the absence of genetic manipulation, however, microbes can perform highly specific tasks which make them indispensable in certain applications. Thus, there is a constant ongoing search in many areas of research for new microbes with specific advantageous properties. The subject invention concerns the discovery of one such microbe.
Weeds are a tremendous problem for farmers throughout the United States and the Caribbean region. Weeds cause a 10-12% loss of value for agricultural products in the United States, the most recent estimate being $20 billion annually (McWhorter, C. G. [1984] Weed Sci. 32:850-855). In Florida, vegetable production alone, losses due to weeds are estimated to be over $100 million. According to the most recent estimates, 41% of the cost of plant protection was for the control of weeds. Herbicides are applied to more acres than fungicides and insecticides combined. Weeds act as alternate hosts for insects, fungi, bacteria, and viruses. They affect man, not only by competing with crop plants, but by poisoning range animals, interfering with right-of-ways and roadways, decreasing forest production, and marring landscapes.
Nutsedges (Cyperus spp.) comprise a group of commonly occurring weeds that are among the most difficult to control. In the Caribbean Basin there are three species which are of most consequence, namely C. rotundus (purple nutsedge), C. exculentus (yellow nutsedge), and C. iria (rice flatsedge). Purple nutsedge has been called the world's worst weed because of its distribution worldwide and its resistance to control measures (Holm, L. G., D. L. Plucknett, J. V. Pancho, and J. P. Herberger [1977] The World's Worst Weeds: Distribution and Biology. University Press of Hawaii, Honolulu). It is a problem in 52 crops in more than 90 tropical and subtropical countries. It is considered a serious weed in the United States and a principal weed in Puerto Rico. Yield reduction due to nutsedge varies. In agronomic crops, yield reduction can be as high as 79%, as was seen in maize. In horticultural crops, yield reduction can reach 80%, as has been seen in beans. Yield reduction in tomato, a very valuable crop in the Caribbean region, can be as high as 53 %. Nutsedges cannot compete with crops if a dense crop canopy is established, making early season control of these weeds essential.
In Florida, purple and yellow nutsedge, and rice flatsedge are problems in virtually every crop grown in the state. In Puerto Rico, the major problem is with purple nutsedge, although the other species are also found. Vegetables, particularly tomato, pumpkin, pepper, and onion, are affected. In the Virgin Islands the major species is also purple nutsedge which causes the greatest problems in vegetables. Purple nutsedge is also widely distributed in other crops throughout the Caribbean Basin.
Many herbicides have been tested for control of purple and yellow nutsedge. Pereira et al. recently reviewed this research (Pereira, W., G. Crabtree, and R. D. William [1987] Weed Technology 1:92-98). Herbicides based on virtually every mode of action have been studied. Examples are: 2,4-D ("control erratic"), atrazine ("control inconsistent"), linuron ("marginal control"), paraquat ("inconsistent"), alachlor and metolachlor ("control temporary"). Some herbicides that have been used successfully include glyphosate, dichlobenil, EPTC, arsenicals, and soil fumigants. Success or failure of a herbicide treatment depends on such factors as nutsedge growth stage at application, soil moisture and temperature, and addition of adjuvants to the spray mixture.
Chemical weed control programs are seriously inadequate for control of this weed. Frequently the weed germinates below the treated zone and avoids herbicide injury. Although many herbicides have been developed and tested in the last three decades, farmers still rely heavily on dinoseb, a herbicide developed in the 1950's. Dinoseb is a contact herbicide that causes injury to some field crops. Alternative approaches include monosodium methanearsonate (MSMA), paraquat, toxaphene, and triazine herbicides, but these chemicals are not registered for use on some crops for reasons of toxicology and/or crop safety.
The use of chemical pesticides in agriculture is currently a major concern in the U.S. Nowhere is this concern more obvious than in the San Joaquin Valley of California, where pesticides are being blamed for an epidemic of cancer in children and young adults (Weisskopf, M. [1988] The Washington Post Weekly Edition 5(47):10-11, Washington, D.C.). New technologies in detection methods are enabling researchers to find pesticides in the environment that were previously thought to be totally degraded. Perhaps the major public concern of the 1980's is protection of groundwater. The Environmental Protection Agency (EPA) estimates that 100,000 of the nation's 1.3 million wells are contaminated with pesticides (Fleming, M. H. [1987] Amer. J. Alternative Agriculture 2:124-130). This has alarmed the general public since 50% of all Americans depend on groundwater wells for their fresh water supplies. Because herbicides are so widely used in agriculture, and because they are often applied directly to the soil, the potential for movement into groundwater by leaching is perhaps greater than any other pesticide. Other inadequacies of chemical controls include lack of residual control, injury to non-target organisms, undesirable residues in harvested products, and carryover in subsequent crops.
There are no selective herbicides which can be used to control these sedges in all crops. Indeed, those herbicides which are available do not always give acceptable control of these weeds. An alternative is offered by the use of microbes which have herbicidal activity specific for the problem weeds, and do not infect desirable plants.
Phatak et al. (Phatak, S. C., M. B. Callaway, and C. S. Vavrina [1987] Weed Technology 1:84-91) have reviewed biological control of purple and yellow nutsedge. Cost effective procedures for the use of insects to control these species have not been developed. Phatak has reported that manipulation of a rust pathogen (Puccinia canaliculata) of yellow nutsedge has reduced stand, tuber formation, and completely inhibited flower formation of this weed. Phatak points out that little research has been directed toward integrating biological and chemical control of nutsedge. It was shown that rust-paraquat (1,1'-dimethyl-4,4'-bipyridinium ion) combinations were much more effective than either treatment alone. Other work indicates that sequential applications of the rust and other herbicides, such as bentazon[3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4-(3H)-one 2,2-dioxide] provided significantly better control than either applied alone. Although this system is promising, there are many aspects that must be investigated, such as spore production and maintenance in storage. Phatak also states that other pathogens should be sought to complement the rust system.
Therefore, the use of bioherbicides is becoming an increasingly important alternative to chemical herbicides. This importance is exemplified by several patents which have been issued for bioherbicides and their use. Some of these patents, by way of illustration, are as follows: U.S. Pat. No. 3,849,104 (control of northern jointvetch with Colletotrichum gloeosporioides Penz. aeschynomene); U.S. Pat. No. 3,999,973 (control of prickly sida [teaweed] and other weeds with Colletotrichum malvarum); U.S. Pat. No. 4,162,912 (control of milkweed vine with Araujia mosaic virus); U.S. Pat. No. 4,626,271 (Cyanobacterin Herbicide); and U.S. Pat. No. 4,915,726 (Biological Control of Dodder).